I installed new kernel linux-image-3.8.0-44-generic and linux-image-3.13.0-73-generic manually and linux-image-3.2.0-96-generic by update. But grub still loads linux-image-3.2.0-89-generic. Grub configured to load default 0 menuentry. 0 menu entry is linux-image-3.13.0-73-generic. But uname -r returned linux-image-3.2.0-89-generic after system load. No any errors in boot.log. If I remove linux-image-3.2.0-89-generic by sudo apt-get remove, system still loads linux-image-3.2.0-89-generic, but networking works incorrectly. Repeat install linux-image-3.2.0-89-generic recover performance. My system is Ubuntu 12.04.5 LTS. Why is this happening?
I am guessing you pressed the down arrow and selected advanced options where you can select which kernel you want to run.
If you have already done that you can uninstall your other kernels although this could be risky if your new kernel doesn't actually work.
You can look at the system log and see if it had any errors. Usually if the kernel doesn't load then it won't boot, but worth checking I suppose.
Usually grub selects the newest kernel(version number) and puts that at the top of the list. Let me know what advanced option says and how it is listing the kernels because it is possible it didn't install as well.